The invention relates to a bar for attaching a steering cylinder of a vehicle to a wheel axle, to a vehicle comprising such a bar and to a process for manufacturing the bar.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipments. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles, such as cars.
In a known manner, a vehicle includes a front axle and a rear axle supporting each two opposite wheels and a steering arrangement for turning the front wheels using a hand-operated steering wheel. In practice, this steering arrangement includes a steering cylinder arranged in front of the wheel axle and receiving a highly pressurized fluid when the driver manipulates the steering wheel. The pressurized fluid generates then a steering force for turning the wheels. The steering cylinder comprises a cylinder body and left and right cylinder rods provided to be extended from and retracted into the cylinder body. The ends of left and right cylinder rods that are opposite to the steering cylinder are respectively hinged to swing links, so as to form a four-bar link structure that is swung by extension and retraction of the steering cylinder rods.
The vehicle further comprises a means for attaching the steering cylinder to the axle beam. This means may be a linking bar. The kinematics of the steering arrangement is such that the steering cylinder may rotate in a horizontal and in a vertical plane. Furthermore, the wheel axle may be distorted over time, which induces a deformation of the steering cylinder and of the linking bar as they are less flexible than the axle. This may involve a steering failure. Consequently, means for attaching the steering cylinder to the axle beam are oversized to absorb both the axle deformation and the motion of the steering cylinder relative to the wheel axle.
US-A-2014/0008885 discloses an agricultural tractor where the steering cylinder is attached to the front wheel axle by means of two connecting rods, respectively attached at the top and at the bottom of the steering cylinder. The connecting rods are articulated at both extremities so that, when the steering cylinder is operated, it may move forwards and rearwards within a predetermined range, while being prevented from moving to the left or to the right of the vehicle. Moreover, two other connecting rods are hinged to the cylinder rods so as to make the coupling of the steering cylinder to the wheel axle more reliable. As a result, the steering cylinder attachment requires a lot of ball joints, which are wearing parts expensive to replace.
It is desirable to provide a bar for attaching a steering cylinder of a vehicle to a wheel axle that can absorb both the axle deformation, without transmitting the axle load to the steering cylinder and the motion of the steering cylinder relative to the wheel axle. In this way, no other connecting rod is required to prevent unwanted rotational movements and less wearing parts are used to attach the steering cylinder to the wheel axle.
To this end, the invention concerns, according to an aspect thereof, a bar for attaching a steering cylinder of a vehicle to a wheel axle. According to an aspect of the invention, the bar is twisted around its longitudinal direction.
Thanks to an aspect of the invention, given that a twisted bar can be easily compressed or extended in its longitudinal direction, it behaves like an elastic spring, thereby absorbing the axle beam deformation and the relative movement of the cylinder with respect to the wheel axle. Consequently, the efforts generated on the axle beam are not transmitted to the steering cylinder, which means that the steering arrangement is not affected either by the axle beam distortion or by the steering cylinder motion. Furthermore, no ball joints are used to attach the steering cylinder to the wheel axle.
According to further aspects of the invention, which are advantageous but not compulsory, such a bar may include one or several of the following features:                The bar includes two end plates for securing the bar to the steering cylinder and to the axle.        Each end plate delimits at least one hole for a fixing screw or a rivet.        The end plates are parallel.        The bar includes a middle plate that is perpendicular to the end plates        The bar is in metal or in composite material.        The bar is bolted or riveted to the steering cylinder and/or to the wheel axle.        The bar is clamped to the steering cylinder and/or to the wheel axle by means of a flange.        
The invention also concerns, according to an aspect thereof, a vehicle, comprising an axle, a steering cylinder and a bar, as previously defined, for attaching the steering cylinder to the axle.
According to further aspects of the invention, which are advantageous but not compulsory, such a vehicle may include one or several of the following features:                In assembled state of the bar in the vehicle, the bar is inclined with an angle inferior to 10° relative to a longitudinal axis of the wheel axle.        The steering cylinder is arranged in front of or behind the wheel axle.        
The invention finally relates to a process for manufacturing a bar for attaching a steering cylinder of a vehicle to a wheel axle, comprising steps consisting in or comprising:                a) cutting out a rectangular plate of metallic material or of composite material, and        b) pivoting one end or pivoting both ends in opposite directions, around a longitudinal axis of the plate.        
According to further aspects of the invention, which are advantageous but not compulsory, such a process may include one or several of the following features:                At step b), both ends are pivoted by the same twisting angle.        At step b), both ends are pivoted by a twisting angle of 90° around the longitudinal axis (X22).        The process includes a step posterior to step a) and anterior to step b) consisting in or comprising: clamping a middle portion of the bar.        